In this proposal we present experiments designed to determine components of the chemical structure of specific permeation mechanisms. Our objectives are to identify specific amino acid residues associated with the functional portions of the proteins responsible for ion conduction and ion transport in the membranes of squid giant axon and barnacle giant muscle fiber. In addition we will determine how the specific residues we identify relate to the normal functioning of the permeation mechanism. Our primary tool for the identification of the chemical structure will be (1) Ionic probes, similar to our previous grant, in which specific ions were used to help elucidate the structure of the ion conductance channels, (2) pH titration: some amino residues have very specific titration points, (3) enzymic modification, to alter exposed protein moieties, and (4) group specific reagents to identify amino acid residues by the reactivity of their side chains. Using these methods we already have significant information about the nature of the inactivation molecule. We know that the inactivation is produced by the guanidino group of an arginine residue blocking the Na ion channel. This group is stabilized in this position by a hydrogen bond linkage between a tyrosine residue in the activation molecule and a hydrogen bond acceptor in the membrane. Additional preliminary information is also available about other conductance and transport mechanisms.